Abstract

A sequence of thinly bedded limestones, dolomites, shales, and sandstones contains evaporitic beds in Counties Leitrim and Cavan, Republic of Ireland. This sequence constitutes the Aghagrania Formation (new name) of B 2 -P 1c age (Upper Visean), with a type section east of Drumshanbo, County Leitrim. The evaporitic beds, which have not previously been recorded from this horizon or locality, are mostly unfossiliferous laminated limestones and dolomites with macrocells and with pseudomorphs after gypsum, anhydrite, and halite. This facies of the Aghagrania Formation also includes evaporitic breccias, and celestite and carbonate replacements of calcium sulphate. Blocks of gypsum in boulder clay, on the shore of Lough Allen, are probably derived from these beds. The evaporitic strata alternate with shales and limestones containing marine faunas, and with unfossiliferous sandstones. All the facies show evidence of shallow water deposition and were probably formed in an area of low relief subjected to transgressions and regressions of a shallow sea. The evaporitic beds may be compared to the dolomite and gypsum deposits of present day tidal flats and associated shallow lagoons. They also resemble certain other occurrences of ancient laminated dolomite and limestone beds which have been recently described and attributed to a tidal flat origin.

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